Inkjet printing systems are in widespread use today. Ink jet printers print dots by ejecting very small drops of ink onto the print medium, and typically include a movable carriage that supports one or more printheads each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
Color ink jet printers commonly employ a plurality of printheads, for example four, mounted in the print carriage to produce different colors. Each printhead contains ink of a different color, with the commonly used colors being cyan, magenta, yellow, and black. Printing devices may have several features or other options, such as print speed, driver selection, dry time and print mode.
Printing devices, such as inkjet printers, use printing composition (e.g., ink or toner) to print text, graphics, images, etc. onto print media. The print media may be of any of a variety of different types, sizes, side-specific coatings, etc. For example, the print media may include paper, transparencies, envelopes, photographic print stock, cloth, plastic, vinyl, special material, etc. Each of these types of print media have various chemical and physical characteristics that ideally should be accounted for during printing; otherwise less than optimal printed products may occur. Additional characteristics may also affect print quality, including print medium size. print medium orientation, and print medium sideness.
One way in which a printing device can be configured to a particular print medium is to have a user make manual adjustments or make program inputs to the printing device based upon these characteristics and factors. One problem with this approach is that it requires user intervention which is undesirable. Another problem with this approach is that it requires a user to correctly identify various characteristics of a particular print medium which the operator may not know. A further problem with this approach is that a user may choose not to manually configure the printing device or may configure the printing device incorrectly so that optimal printing still does not occur in spite of user intervention. This can be time-consuming and expensive depending on when the configuration error is detected and the cost of the particular print medium.
It would therefore be an advantage to be able to automatically read media characteristic information automatically and without requiring user input, by having the media communicate directly to the printing device.
Inkjet printers can support printing images on a variety of print media types, including plain paper, coated paper, clear film media, as well as others. There are several known methods for marking paper media with machine readable indicia, including visible indicia and indicia not visible to the human eye under normal ambient lighting conditions.
Readable indicia on clear film can be printed to be visible or invisible to humans. Compounds which reflect or fluoresce light at non-visible wavelengths will still be slightly visible to humans. This visibility is caused, e.g., by a difference in the refractive index of the compound and the clear film.
Indicia typically includes marks on a media substrate that either absorb, reflect or emit light. In all cases, for an indicia to be machine readable, there must be enough difference in radiation returned from marked areas of indicia and unmarked areas on the substrate that a useful signal is generated.
Indicia placed on clear film are difficult to read using an optical sensor. With a clear background, as in the case of clear film, a poor contrast is produced between the indicia and the background. If the indicia are made to absorb light, they cannot be detected at all. Clear film reflects only a small portion of the incident light. Placing a light absorbing compound on the indicia only causes this small portion of reflected light to be absorbed. The difference in signal is well below the noise level. If fluorescing indicia are used, then the level of fluorescence is greatly reduced by a clear background. This difference in signal strength is shown in FIGS. 1A and 1B, showing the respective situations when a fluorescent material is placed on the surface of a sheet of white paper and on clear film. With the white paper, most of the incident and fluorescent light is reflected upwardly. Some of the reflected fluorescent light will enter the sensor to provide signal. With the clear film, a large portion of the incident and fluorescent light will not be reflected up to the sensor. The light will either pass through the film (D) or be lost to total internal reflection.
A white background can be placed in the printer behind the clear film media at a point where the indicia will be read by the sensor. This helps to create a contrast, but fluorescing compounds still produce a poor signal due to the inefficiencies illustrated in FIG. 1. The small air gap between the clear film and the white background will create an interface at which significant light will be lost.